In the realm of on demand video, viewers (also referred to as hosts and participants) can subscribe to individual programs on various channels. If the video is being relayed using Internet Protocol Television (IPTV) technology, the set-top boxes (STBS) in the homes need to send subscription messages to a multicast router using IGMP report messages. Upon receiving the subscription messages (known as IGMP report messages), the multicast router will join the participant to an IGMP group of participants for that program and begin streaming the video to the STB. IGMP and IGMP report messages are well known in the art and described more fully in Request for Comments (RFC) 3376, “Internet Group Management Protocol, Version 3,” October 2002.
Multicast domains administered independently by separate multicast routers at the same geographical location cater to different sets of participants that may be viewing the same program at the same time provided by a single multicast source (also referred to as a multicast server). In such a situation, it was not previously possible to a get a count of the actual number of participants that are participating in an IGMP group because no single multicast router handled all of the participants for a single group as the participants are in different multicast domains. Further, because of the nature of multicast networks, the multicast server does not know of the participants in the IGMP group but rather knows of the multicast router requesting the video for its participants.
Therefore, it is desirable to provider a mechanism for tracking all participants in an IGMP group without requiring communication between the multicast routers and without modifying existing STBS.